An amino acid ionic liquid-based biphasic solvent with low viscosity, small rich-phase volume, and high CO2 loading rate for efficient CO2 capture

Abstract

In order to achieve efficient CO2 capture, a novel biphasic solvent based on diethylenetriamine serine ionic liquid/polyethylene glycol dimethyl ether/water ([DETA][SER]/NHD/H2O) was developed. This study achieved low viscosity by weakening the hydrogen bonding and van der Waals interactions within the pure ionic liquid (IL) by adding NHD and H2O to [DETA][SER]. Additionally, due to the low polarity and fewer hydrogen bonds formed by NHD, it is separated. The formation of a tight hydrogen bond network in the rich-phase after the reaction enables the enrichment of the product. Based on this, the optimal mass ratio of [DETA][SER]/NHD/H2O is determined to be 20 wt%/40 wt%/40 wt%. The viscosity of this solvent is 7.82 mPa·s, with a total absorption load of 1.26 mol·mol−1 IL, where the rich-phase load accounts for 99 % of the total load and occupies only 37 % of the volume. The mechanism of CO2 capture was investigated using 13C NMR, revealing the formation of zwitterions from the reaction of the primary amines on [DETA]+ and [SER]− with CO2. Subsequently, proton transfer and hydrolysis of the carbamate esters were observed. Notably, NHD was found to promote phase separation without participating in chemical reactions. These findings demonstrate the potential of this biphasic solvent system as a high-capacity solution for CO2 capture.